Mesoporous silica as discussed by: T. Yanagisawa et al. (1), C. T. Kresge et al. (2), and J. S. Beck et al. (3), (listed in the reference list below and incorporated herein by reference) is an important class of self-assembled inorganic materials consisting of regularly arranged mesoporous channels in the amorphous silicon dioxide network. Because of their large specific surface area, high pore volume, uniform pore diameter and high thermal stability, mesoporous silica has been envisaged to be a promising material in adsorption, catalysis, and ultrafiltration, so also as a host for deposition of clusters, nanodots and nanowires etc.
Mesoporous silica exhibiting lamellar, hexagonal (p6 mm), or cubic (1a3d, Im3m, Pm3n, etc.) structures and presenting a host of pore arrangements have already been prepared under different preparative conditions. See T. Yanagisawa et al. (1), C. T. Kresge et al. (2), J. S. Beck et al. (3), D. Zhao et al (4), D. Zhao et al. (5), and H. Yang et al. (6), (all listed below and all incorporated herein by reference). It has been realized that the control over the particle morphology and the internal mesoporous architecture could open up new possibilities for their usage as a carrier for functional molecules for advanced applications-in lasers and optics. For example, see B. J. Scott et al. (7). F. Marlow et. al.. (8), and I. Sokolov et al. (9), all listed in the reference list below and all hereby incorporated herein by reference.
Previously, mesoporous silica particles of different morphology have been synthesized using alkyl orthosilicates as silica source together with ionic or block copolymer surfactants as structure directing agents (SDAs) under basic or acidic preparative conditions. See G. A. Ozin et al. (10). Q. Huo et al. (11), S. Schacht et al. (12), X. Pang et al. (13), K. Kosuge et al. (14) X. Pang et al (15), S. Han et al. (16), S. P. Naik et al. (17), and Y. S. Lin et al (18), all listed in the reference list below and all hereby incorporated herein by reference. However, due to their high costs, storage and handling problems, replacement of alkysilicates by other economical and more robust sources of silica is much desired to realize their anticipated commercial applications. See A. Berggren et al. listed in the reference list below and hereby incorporated herein by reference. Sodium silicates represent an example of economical and robust sources of silica. There have already been several reports on the synthesis of mesoporous silica fibers and spheres using sodium silicates as a silica source. See X. Pang et al., K. Kosuge et al., X. Pang et al., S. Han et al., and S. P. Naik et al. listed in the reference list below and all hereby incorporated herein by reference. Nonetheless, many of these methods involve use of organic solvents or mixtures of surfactants and complex procedures for the synthesis of mesoporous silica particles. Moreover, synthesis of well-formed mesoporous silica particles having a circular internal architecture and pore channels running around the particle axis using sodium silicate as a silica source has not been reported using inorganic silica sources. Mesoporous silica with such morphology is useful in applications involving maximum retention of the occluded species inside the mesostructure for an extended period of time. See I. Sokolov et al. listed in the reference list below and hereby incorporated herein by reference.